To discover and develop new methods and interpretive criteria in the biological applications of SEM. For most studies described herein, tissue culture cells are grown as monolayers on glass coverslips, fixed by the addition of an equal volume of buffered 6% glutaraldehyde to the medium and processed appropriately for SEM. To evaluate the impact of environmental conditions on cell form and surface morphology, HBT-3 cells (a human breast tumor line) were grown on various substrates, in various media and buffered salt solutions, and in media supplemented with various concentrations of fetal calf serum (FCS). Studies of cellular topography in relation both to interphase stages of the cell cycle and to neoplastic state were carried out on established mouse fetal lines derived from a common single cell.